Ohio, Michigan and Ontario are expected to sign an agreement Saturday that would require each to reduce phosphorous runoff that fuels toxic algae on Lake Erie.

The goal is to cut phosphorous from fertilizer, wastewater plants and other sources getting into the lake’s western basin by 40 percent by 2025, which would help stop the annual summer blooms of toxic blue-green algae on Lake Erie.

The algae, which produces a toxin called microcystin, can sicken people and pets and threatens Lake Erie’s tourism industry. Last August, the toxin contaminated the city of Toledo’s drinking water supply for three days, affecting nearly 500,000 water customers in Ohio and Michigan.

Ohio Lt. Gov. Mary Taylor, Michigan Gov. Rick Snyder and Ontario Premier Kathleen Wynne are expected to sign the agreement Saturday in Quebec City in Canada during a meeting of the Great Lakes and St. Lawrence Council of Governors and Premiers. Ohio Gov. Kasich is not attending the meeting.

Although the states and Ontario have already started initiatives to reduce runoff, working together will better help the health of the lake, Wynne said.

“I don’t think that we can do that in isolation from each other,” she said. “That will hold all of our feet to the fire to work with our jurisdictions.”

The planned 40 percent reduction comes after the Ohio Lake Erie Phosphorous Task Force II , which studied the algae problem and looked at potential solutions, recommended in 2013 that phosphorous loading to Lake Erie be cut by that amount.

“This is a goal we need to have,” Snyder said during a news conference Friday. “I believe it’s an achievable goal. I think a lot of good practices have already started, but I think we can do more partnerships.”

Although agriculture has been identified as the biggest source of the phosphorous loading, wastewater plants, faulty septic systems and other sources contribute.

Earlier this year, Ohio legislators passed a law that bans farmers from spreading fertilizer and manure — which contain phosphorous — on frozen and rain-soaked fields. It also will end within five years the dumping of sediment from dredging into Lake Erie, which also has been blamed for contributing to algae.

And an Ohio law requiring farmers to take a state-run certification course that teaches them how much fertilizer is needed for certain areas of land and when it should be applied takes effect in 2017.

Scientists made a very early prediction last month that the algae would not be as bad this year as it was in the record-setting 2011 bloom and heavy bloom of 2013. But heavy rains could change that prediction, and there isn’t a way to forecast whether toxins from algae will again foul drinking water.

The National Oceanic and Atmospheric Administration is expected to release its annual summer algae forecast in early July at Ohio State University’s Stone Laboratory on Gibraltar Island near Put-in-Bay.

A type of harmful algae, called planktothrix, has already covered much of the Sandusky Bay, said Doug Kane, associate professor of biology at Defiance College, who also teaches at Stone Lab. This isn’t unusual because planktothrix is normally blooming heavily at this time of year on the bay, which is the southernmost part of the Great Lakes and warms up the fastest.

Its presence is a concern because it can produce toxins, including microcystin, Kane said. Planktothrix is a greenish-brown algae that thrives in warmer temperatures, which explains why it is found on the bay, he said.